Because injury to the human heart results in irreversible loss of myocardium, insults such as infarction often lead to heart failure, susceptibility to arrhythmia, and death. In stark contrast, zebrafish are able to regenerate functional myocardium following injury by cardiomyocyte proliferation. Recently, a low grade of cardiomyocyte proliferation has been described in the adult mammalian heart. Therapies to augment cardiac regeneration following injury are attractive strategies to prevent human heart failure. However, the complement of factors that facilitate regeneration are unknown. Here, we propose the use of unbiased proteomic profiling and cell- type specific gene expression profiling to identify the extracellular factors that orchestrate zebrafish heart regeneration. Our preliminar work has identified brain natriuretic peptide (nppb) as a secreted factor that is spatiotemporally related to heart regeneration. We will generate novel transgenic fish to conditionally overexpress nppb and a dominant negative form of its receptor in specific cell lineages using Cre/Lox technology. These experiments will allow for the determination of autocrine and paracrine roles for nppb and serve as a template for future work to study the mechanism of action for other factors identified. Finally, we will assess conservation of these factors followin injury to the regenerative neonatal mouse heart and the poorly- regenerative adult mouse heart. Factors preferentially induced in regenerating neonatal mouse hearts compared to adult mouse hearts represent candidate biomarkers for heart regeneration. Markers of cardiac injury and regeneration that are conserved following cardiac injury in zebrafish and mice will then be measured in a repository of plasma obtained from patients following myocardial infarction. Marker levels will be tested for relation to human cardiovascular outcomes. The proposed experiments will identify factors that coordinate zebrafish heart regeneration and potential factors to therapeutically augment mammalian cardiomyocyte proliferation. In addition, our focus on secreted factors with regeneration will contribute to the development of a biomarker toolbox for future epidemiologic studies to understand the role of regeneration in human cardiovascular disease. Over the next several years, I hope to become an independent clinician-scientist focusing on heart regeneration. I ultimately hope to become an established investigator studying how variation in cardiac homeostasis affects the development of cardiovascular disease, specifically heart failure. The outlined experiments will provide a foundation for future mechanistic work to better understand the factors the facilitate regeneration and for a set biomarkers to understand how cardiac homeostasis affects cardiovascular outcomes following infarction. My work will be mentored by Dr. Kenneth Poss, PhD, a pioneer and leader in regenerative biology. We will collaborate with the Duke Clinical Research Institute, allowing for the ideal training experience for a translational research career.